High density storage disks are configured with layers of materials that provide the required data stability for storage. The magnetic properties of the media require a softening when writing to the disk to change the bit state. Energy Assisted Magnetic Recording (EAMR) device or Heat Assisted Magnetic Recording (HAMR) technology provides heat that is focused on a nano-sized bit region when writing onto a magnetic storage disk, which achieves the magnetic softening. A light waveguide directs light from a laser diode to a near field transducer (NFT). The NFT focuses the optical energy to a small spot on the target recording area which heats the magnetic storage disk during a write operation.
EAMR/HAMR uses a controlled magnitude of laser diode power for the magnetic softening at the disk. During operation with temperature and current change, the laser diode gain spectrum shifts causing laser mode hops. Because different longitudinal modes have different spectral positions, the power magnitude changes, which creates recording noise. The delta between longitudinal modes is particularly significant in a case of optical feedback from optical elements located at a distance greater than 100 microns from the laser diode facet. For example, the laser diode may receive reflection from a near field transducer and the magnetic storage disk, which will have different phase shift for different modes, such that laser power will change with mode hopping.